Mapping the adsorption dynamics of core-shell particles at liquid-liquid interfaces with optical tweezers

Once colloidal particles adsorb to liquid interfaces, they stick irreversibly, lowering interfacial energy by millions of kBT. However, spontaneous adsorption is often hindered by an electrostatic energy barrier, requiring charge screening (e.g., salt) for attachment. Here, we show that coating colloidal particles with high-molecular-weight polymers enables them to overcome this barrier and spontaneously jump into the liquid interface. Using optical tweezers, we track single-particle adsorption dynamics at a dodecane–water interface, revealing how polymer shells facilitate interfacial attachment. Our model system consists of silica cores coated with poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) with controllable molecular weight. Bare silica particles do not adsorb without salt, but polymer-coated ones jump in upon polymer contact with the interface. Similar behavior is observed for other polymers, suggesting that adsorption is dictated by polymer properties rather than specific chemistry. These insights provide new strategies for designing stimuli-responsive emulsions.